首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   10618篇
  免费   454篇
  国内免费   82篇
电工技术   204篇
综合类   78篇
化学工业   2784篇
金属工艺   217篇
机械仪表   404篇
建筑科学   397篇
矿业工程   20篇
能源动力   662篇
轻工业   1128篇
水利工程   197篇
石油天然气   149篇
武器工业   5篇
无线电   1061篇
一般工业技术   1741篇
冶金工业   218篇
原子能技术   70篇
自动化技术   1819篇
  2024年   183篇
  2023年   255篇
  2022年   382篇
  2021年   729篇
  2020年   643篇
  2019年   824篇
  2018年   806篇
  2017年   761篇
  2016年   769篇
  2015年   440篇
  2014年   727篇
  2013年   1062篇
  2012年   674篇
  2011年   748篇
  2010年   490篇
  2009年   412篇
  2008年   248篇
  2007年   185篇
  2006年   151篇
  2005年   102篇
  2004年   104篇
  2003年   61篇
  2002年   61篇
  2001年   29篇
  2000年   23篇
  1999年   25篇
  1998年   25篇
  1997年   20篇
  1996年   24篇
  1995年   23篇
  1994年   12篇
  1993年   17篇
  1992年   11篇
  1991年   17篇
  1990年   16篇
  1989年   13篇
  1988年   8篇
  1987年   7篇
  1986年   8篇
  1985年   8篇
  1984年   14篇
  1983年   12篇
  1982年   4篇
  1981年   3篇
  1980年   2篇
  1979年   6篇
  1978年   3篇
  1977年   3篇
  1973年   2篇
  1967年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Pomegranate juice was concentrated by conventional heating and microwave heating at different operational pressures (12, 38.5, and 100 kPa), and their effects on evaporation rate and quality attributes of concentrated juice were investigated. The final juice concentration of 40° Brix was achieved in 140, 127, and 109 min at 100, 38.5, and 12 kPa, respectively, by using conventional heating. Applying microwave energy decreased required times to 118, 95, and 75 min. The changes in color, anthocyanin content, and antioxidant capacity during concentration processes were investigated. L*, a*, and b* parameters were measured to estimate the intensity of color loss. All Hunter color parameters decreased with time. Results showed that the degradation of color, anthocyanins, and antioxidant activity were more important in conventional heating compared to microwave heating method. Degradation rates increases by increasing process pressure. A first-order kinetics model was applied to modeling changes in total solid content, anthocyanin content, and antioxidant capacity.  相似文献   
12.
Behavior of normal strength concrete columns reinforced with a new reinforcement, termed Prefabricated Cage System (PCS) is investigated. A total of 16 small-scale PCS and rebar reinforced column specimens were constructed and tested under monotonic axial displacement. The experimental results indicate that the overall behavior of rebar and PCS reinforced specimens are comparable prior to achieving the peak column load. In general, PCS specimens are more ductile and absorb more energy than similar rebar specimens after the peak load is reached. The effect of different parameters, such as the steel tube thickness, number of longitudinal reinforcements, transverse steel spacing, and crossties on the specimens’ strength and deformation capacity are investigated. A confined concrete model is proposed and used to predict the load–displacement response. The theoretical load–displacement relations obtained from the proposed model are compared with those obtained from the Mander et al. (J Struct Eng 114(8):1804–1826, 1988) confinement model.  相似文献   
13.
The use of nitrilotriacetic acid end‐functionalized polystyrenes (NTA‐PS) as a multifunctional nanocarrier for the aqueous dispersion of CdSe, γ‐Fe2O3 and gold nanoparticles (NPs) is described. When the amphiphilic end‐ functionalized polystyrenes and NPs are dissolved together in tetrahydrofuran, the addition of water causes the spontaneous formation of micellar aggregates, resulting in the successful encapsulation and aqueous dispersion of NPs. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), photoluminescence (PL) spectroscopy, and vibrating sample magnetometer (VSM) are used to characterize the structure and properties of the NPs‐containing micellar aggregates (nanocarrier). After complexation of Ni2+ with NTA on the surface of the nanocarrier containing γ‐Fe2O3, specific binding between Ni‐NTA complex and histidine‐tagged (His‐tagged) proteins enables selective separation of His‐tagged proteins using a magnet.  相似文献   
14.
The first results of the movable electrode biasing experiments performed on the IR-T1 tokamak are presented. For this purpose, a movable electrode biasing system was designed, constructed, and installed on the IR-T1 tokamak, and then the positive voltage applied to an electrode inserted inside the tokamak limiter and the plasma current, poloidal and radial components of the magnetic fields, loop voltage, and diamagnetic flux in the absence and presence of the biased electrode were measured. Results compared and discussed.  相似文献   
15.
16.
17.
Renewable energy resources show great promise in Palestine. Solar, wind, biogas and geothermal energy resources are the main areas where research and pilot projects are being concentrated (2000–2005). More than 95% of Palestinians use solar energy for domestic water heating so renewable energy is something that many people in the country are already very aware. Consequently, use of renewable energy resources presents a strategic goal for the Palestinian energy authority in order to achieve some degree of economic independence. It aims to minimize the dependence on traditional energy resources that are too expensive and politically controlled. Awny Naim and Mohammad R Al-Agha, Palestinian Renewable Energy Society describe the current situation in the region.  相似文献   
18.
Tobacco leaves (Nicotiana tabacum L.), agricultural soil and pollute irrigated lake water samples were collected during 2005–2006 and analyzed for Cd and Ni by electrothermal atomic absorption spectrometry (ETAAS). A simple and efficient procedure was investigated for the complete decomposition of tobacco leaves using ultrasonic assisted acid pseudo-digestion method (UPDM). A Plackett–Burman experimental design was used as a multivariate strategy for the evaluation of seven factors/variables at once, while central composite were used to found optimum values of significant variables. The accuracy of the proposed methods was assessed by analyzing certified reference (CRM); Virginia tobacco leaves (CTA-VTL-2). The results being compared with those obtained by conventional wet acid digestion method. The result obtained by optimized method showed good agreement with the certified values and sufficiently high recovery 97.8 and 98.7% for Cd and Ni, respectively. Under optimal conditions, the detection limits (3σ) were evaluated to be 0.019 μg g−1 for Cd and 0.37 μg g−1 for Ni. The proposed method was successfully applied to the determination of Cd and Ni in raw, processed tobacco and different branded cigarettes samples.  相似文献   
19.
20.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号